Apache Solr allows to swap two cores around for non-Cloud configurations. They take each other’s name, so it is a good way to push an updated core into a production without downtime.

But an interesting question is how this is achieved. Normally, core name is it’s directory name too. So, does Solr rename the directory on the filesystem too?

Not really! Instead name property in the core.properties file is updated to use the name of the other core. Usually that property is used to give an alternave name of the core for when the directory naming conventions are not suitable.

The gotcha is – of course – that you still have two directories with right looking names for the cores you see in the Admin UI. So, it is very easy to forget that extra redirection/rename step when troubleshooting somebody else’s – or even your own old – setup.

I presented at the Lucene/Solr Revolution 2014 in November, comparing Solr and Elasticsearch. The target audience was a technical person who wants to understand how similar (mostly Lucene) concepts are expressed in these two products.

The presentation was only 30 minutes, so I could not go into the subject as deep as I initially hoped. But the room was more than full and people came up to me afterwards saying that they really liked the comparison and found it helpful.

Leanpub is a platform for publishing books that gives author control and tools beyond those available from traditional publishers. I used it to test an idea for a Solr Clients book and was able to validate its lack of traction without spending a cent.

One of the great features of Leanpub is that a book can be updated and the readers get notified of the new version. Consequently, it is sometime useful to keep the old versions around for the author and sometimes even for the readers.

This feature is not currently present in Leanpub, but we can add that with a bit of a glue from Zapier – web automation service. This is especially useful if you are using GitHub to edit your book with automatic preview and want a full end-to-end edit-preview experience without having to touch the Leanpub website.

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If you are using Solr, you should check out Solr Start. It has a full list of UpdateRequestProcessors, every Analyzer, Tokenizer, and Filter shipped with Solr and a searchable version of Lucene and Solr Javadocs.